ilogb (3)
Leading comments
Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
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NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating-point valueSYNOPSIS
#include <math.h>
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
ilogb():
-
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
ilogbf(), ilogbl():
-
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
These functions return the exponent part of their argument as a signed integer. When no error occurs, these functions are equivalent to the corresponding logb(3) functions, cast to int.RETURN VALUE
On success, these functions return the exponent of x, as a signed integer.If x is zero, then a domain error occurs, and the functions return FP_ILOGB0.
If x is a NaN, then a domain error occurs, and the functions return FP_ILOGBNAN.
If x is negative infinity or positive infinity, then a domain error occurs, and the functions return INT_MAX.
ERRORS
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.The following errors can occur:
- Domain error: x is 0 or a NaN
- An invalid floating-point exception (FE_INVALID) is raised, and errno is set to EDOM (but see BUGS).
- Domain error: x is an infinity
- An invalid floating-point exception (FE_INVALID) is raised, and errno is set to EDOM (but see BUGS).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| ilogb(), ilogbf(), ilogbl() | Thread safety | MT-Safe |
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.BUGS
Before version 2.16, the following bugs existed in the glibc implementation of these functions:- *
- The domain error case where x is 0 or a NaN did not cause errno to be set or (on some architectures) raise a floating-point exception.
- *
- The domain error case where x is an infinity did not cause errno to be set or raise a floating-point exception.